Assertion : d-block metals have generally high M.P. 

Reason: Greater number of electrons from $(\mathrm{n} - 1)d$ in addition to ns electrons are involved in the interatomic metallic bonding

Because more electrons from  $(n-1)d$ in addition to ns electrons are involved in the interatomic metallic bonding, d-block metals have higher melting and boiling temperatures.

Except for anomalous values of $\mathrm{Mn}$ and $\mathrm{Tc}$, the melting temperatures of d-block increases to $d^5$ and decrease steadily as the atomic number rises.

Assertion is True, reason is True,  reason is a correct explanation for Assertion.